A wireless communication system has evolved to support a high data rate in order to satisfy a demand for wireless data traffic which continuously increases.
A 4th generation (4G) wireless communication system has developed various schemes to enhance an spectral efficiency for increasing a data rate, however, it is difficult to satisfy a wireless data traffic demand which remarkably increases using only the various schemes.
So, various schemes to satisfy the wireless data traffic demand which remarkably increases have been proposed, and a typical scheme is a scheme which uses a very wide frequency band, i.e., a ultra-wideband frequency.
In a frequency band (<5 GHz) which a mobile communication cellular system currently uses, it is very difficult to guarantee a wide frequency band, so there is a need for guaranteeing a ultra-wideband frequency at a frequency band which is higher than the frequency band which the mobile communication cellular system currently uses.
In a conventional wireless communication system, the higher a transmission frequency used for a wireless communication becomes, the more increased propagation path loss becomes. Due to this propagation path loss, a wave propagation distance becomes relatively short, this results in decreasing a service coverage.
So, various schemes for solving a service coverage decrease due to an increase of propagation path loss, i.e., various schemes for mitigating propagation path loss and increasing a propagation distance have been proposed, and a typical scheme is a beam forming scheme.
A detailed description of the beam forming scheme will be followed.
The beam forming scheme is classified into a transmission beam forming scheme and a reception beam forming scheme, and the transmission beam forming scheme and the reception beam forming scheme will be described below.
Firstly, the transmission beam forming scheme is a scheme that centers a signal transmitted through each of a plurality of antennas on a specific direction. Here, a set of the plurality of antennas is called an “array antenna”, and each of the plurality of antennas included in the array antenna is called an “antenna element”. If the transmission beam forming scheme is used, a propagation distance of a signal may be increased, and a signal is not almost transmitted in other direction other than a related direction. So, an interference which affects other user equipments (UEs) other than a related UE which receives the signal is remarkably decreased.
Secondly, the reception beam forming scheme is a scheme that centers a reception of a wave using an array antenna on a specific direction to increase a sensitivity of a signal which is received from a related direction, exclude a signal which is received in a direction other than the specific direction from a signal which a UE should receive, and block an interference signal.
The higher a transmission frequency used for transmitting a signal becomes, the shorter a wave length of a wave becomes. If an antenna is configured at half-wave length intervals, an antenna array may be configured in order to include more element antennas within the same area. So, a wireless communication system which operates in a high frequency band may acquire an antenna gain which is relatively high compared to a wireless communication system which uses a beam forming scheme in a low frequency band. The beam forming scheme may be more advantageous in a high frequency band.
In a current wireless communication system, it is well known that a relatively high antenna gain may be acquired using a beam forming scheme, however, there is no scheme for measuring a channel quality using the beam forming scheme and feeding back the measured channel quality.